The present invention generally relates to thermal metrology, and in particular, to the determination of the quantity of heat which passes through a wall per unit of time and surface.
It is particularly concerned with an apparatus for measuring thermal flux or heat transfer, i.e., a thermal fluxmeter or heat flowmeter or heat transfer meter, used for measuring thermal conductivity or resistance, for example of insulation materials or construction elements.
It is known that measuring certain thick and light fibrous insulating materials necessitates the use of measuring apparatus having a large measuring surface.
In order to carry out these measurements, several types of thermal fluxmeters have already been developed. One of these known fluxmeters contains a substratum of an electrical insulating material with a network of transverse orifices extended therethrough and several thermocouples serially connected. The hot and cold junctures of the thermocouples are placed respectively on opposite sides of the substratum while the respective conductors of each thermocouple extend through the substratum by way of the adjacent orifices, on the one hand to connect the hot and cold junctures to each other, and, on the other hand to serially connect the thermocouples. It is thus possible to distribute to the edges of this serial set-up an electrical voltage which is the sum of the electromotive forces generated by all the thermocouples and which is a function of the difference between the respective temperatures at opposite sides of the substratum.
In a manner well known per se, and by using the value of this voltage, the thermal flux passing through the fluxmeter can be determined.
In one known arrangement of a fluxmeter having the above construction, the conductors used for connecting each thermocouple and for connecting the thermocouples to each other are pieces of wire which must be manually inserted into the orifices of the substratum and then conveniently soldered to each other in places which are predetermined by small conducting plates secured in place by electroplating on the two sides of the substratum.
This prior fluxmeter has certain disadvantages as follows:
Manufacturing such a fluxmeter requires considerable manual fabrication, because of the fact that the pieces of wire must be inserted by hand and the solderings done one after another, likewise by hand. The time required for manufacturing is consequently longer as more thermocouples are added. In addition, the solderings on the small plates creates an overthickness condition which affects the evenness of the hot and cold sides, necessitating the pressing of the parts in a mold in order to finally obtain a fluxmeter with two flat and parallel sides. In addition, in the case where the wires are not fine enough, thermal bridges appear, and the thermal conductivity thus created distorts the results of the measurements to a certain extent.